The present disclosure relates to a tool for machining a workpiece which is preferably designed as an internal turning tool and is suitable for machining inside surfaces of bores, for example, for recess turning of circumferential grooves into the bore wall, for precision turning of the bore wall, for thread turning in a bore wall or the like.
An exemplary tool of this type is disclosed, for example, in DE 89 02 529 U1 and has already been marketed by the Applicant for years under the name “Horn Supermini®”. Said tool system offers the possibility, depending on the application, of fastening the most varied types of cutting inserts in the tool holder. The tool system is suitable both for grooving and for external turning of bores and for axial grooving and thread turning. On account of the geometry and size of the cutting insert and of the tool holder, the named tool system is suitable, in particular, for machining small bores, for diameters as small as 0.2 mm.
The named tool or tool system is distinguished, in particular, in that the cutting insert comprises a clamping portion which is insertable into the cutting insert receptacle in the tool holder and is clampable on the tool holder by means of a clamping screw. In the case of the solution known up to now, the clamping screw is inserted into the tool holder from above, perpendicularly to the longitudinal axis of the holder and of the cutting insert. In the mounted state of the tool, the clamping screw presses from above directly onto the cutting insert and fixes it, in this case, in the cutting insert receptacle of the tool holder. A notch, in which the clamping screw engages or pushes, is provided for this purpose on the top surface of the cutting insert shank. Releasing the cutting insert from the tool holder can be performed in a very simple manner by releasing the clamping screw such that replacing the cutting insert is relatively simple and can be done in a short time.
In contrast to “conventional” turning tools, the cutting insert receptacle provided in the tool holder in the case of the tool of the above-named type is realized as a type of blind hole or cup-shaped recess. The cutting insert is therefore not clamped between two expandable clamping fingers as in the case of many turning tools for groove turning but is inserted into a recess and fixed on the tool holder by means of the above-named clamping screw. In the mounted state of the tool, the clamping portion of the cutting insert is consequently surrounded, preferably fully, transversely with respect to the longitudinal direction thereof along the entire circumference of the tool holder.
Although the tool disclosed in DE 89 02 529 U1 has been proven in practice, it has been possible over the years to ascertain a few disadvantages of said tool system. In the case of the solution known up to now, the axial abutment between the cutting insert and the tool holder is effected as a result of the holder-side end of the cutting insert shank abutting against an axial contact surface on the tool holder, which contact surface is aligned orthogonally with respect to the longitudinal direction of the cutting insert or tool holder. The distance between the axial abutment and the cutting edge arranged on the opposite end of the cutting insert is consequently relative large. The clamping screw, which presses onto the cutting insert shank orthogonally with respect to the longitudinal direction of the cutting insert or tool holder, contributes to the fact that the cutting insert is stressed by “buckling” during the machining of the workpiece. Apart from this, the clamping screw compresses the cutting insert somewhat within the fitting tolerance. Since, when the clamping screw is tightened, the cutting insert can be deformed elastically, this can result in deviations in the center height, which has a negative effect on the precision of the tool. The notch provided in the cutting insert shank, in which the clamping screw engages, additionally reduces the stability and strength of the cutting insert shank.